From patchwork Wed Mar 10 22:00:19 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yu-cheng Yu X-Patchwork-Id: 12129525 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 00603C433DB for ; Wed, 10 Mar 2021 22:01:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9A35F64FD5 for ; Wed, 10 Mar 2021 22:01:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9A35F64FD5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 281968D021A; Wed, 10 Mar 2021 17:01:17 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 230D28D0219; Wed, 10 Mar 2021 17:01:17 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 034A08D021A; Wed, 10 Mar 2021 17:01:16 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0095.hostedemail.com [216.40.44.95]) by kanga.kvack.org (Postfix) with ESMTP id D7E598D01ED for ; Wed, 10 Mar 2021 17:01:16 -0500 (EST) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 9A45B12D7 for ; Wed, 10 Mar 2021 22:01:16 +0000 (UTC) X-FDA: 77905336152.04.B2A32E7 Received: from mga12.intel.com (mga12.intel.com [192.55.52.136]) by imf10.hostedemail.com (Postfix) with ESMTP id 5496B40001DE for ; Wed, 10 Mar 2021 22:01:12 +0000 (UTC) IronPort-SDR: 9cuav8hyFk/nYA2UJS3Jl5tMTjhBqjWUelpuyYM2Jdy7QqLLFpMVwQ1pABlo1pBvEAxEDRa1vK /guk5N26Ddyg== X-IronPort-AV: E=McAfee;i="6000,8403,9919"; a="167846405" X-IronPort-AV: E=Sophos;i="5.81,238,1610438400"; d="scan'208";a="167846405" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Mar 2021 14:01:12 -0800 IronPort-SDR: wic0vLGBRReWyCOfcJylyJZ9tYqpZTERU9U34wyraBWe6yWaYq10WVHi644Cr1Yt082bca9los AFEUZde2q3Ug== X-IronPort-AV: E=Sophos;i="5.81,238,1610438400"; d="scan'208";a="403847576" Received: from yyu32-desk.sc.intel.com ([143.183.136.146]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Mar 2021 14:01:12 -0800 From: Yu-cheng Yu To: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu , Haitao Huang Cc: Yu-cheng Yu Subject: [PATCH v22 01/28] Documentation/x86: Add CET description Date: Wed, 10 Mar 2021 14:00:19 -0800 Message-Id: <20210310220046.15866-2-yu-cheng.yu@intel.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20210310220046.15866-1-yu-cheng.yu@intel.com> References: <20210310220046.15866-1-yu-cheng.yu@intel.com> MIME-Version: 1.0 X-Stat-Signature: 95dncg7wifdfjooiq7akmzwrdj5jzy7x X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 5496B40001DE Received-SPF: none (intel.com>: No applicable sender policy available) receiver=imf10; identity=mailfrom; envelope-from=""; helo=mga12.intel.com; client-ip=192.55.52.136 X-HE-DKIM-Result: none/none X-HE-Tag: 1615413672-159154 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Explain no_user_shstk/no_user_ibt kernel parameters, and introduce a new document on Control-flow Enforcement Technology (CET). Signed-off-by: Yu-cheng Yu Reviewed-by: Kees Cook --- .../admin-guide/kernel-parameters.txt | 6 + Documentation/x86/index.rst | 1 + Documentation/x86/intel_cet.rst | 136 ++++++++++++++++++ 3 files changed, 143 insertions(+) create mode 100644 Documentation/x86/intel_cet.rst diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 04545725f187..bc79e54be91e 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3220,6 +3220,12 @@ noexec=on: enable non-executable mappings (default) noexec=off: disable non-executable mappings + no_user_shstk [X86-64] Disable Shadow Stack for user-mode + applications + + no_user_ibt [X86-64] Disable Indirect Branch Tracking for user-mode + applications + nosmap [X86,PPC] Disable SMAP (Supervisor Mode Access Prevention) even if it is supported by processor. diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst index 4693e192b447..cf5250a3cc70 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -21,6 +21,7 @@ x86-specific Documentation tlb mtrr pat + intel_cet intel-iommu intel_txt amd-memory-encryption diff --git a/Documentation/x86/intel_cet.rst b/Documentation/x86/intel_cet.rst new file mode 100644 index 000000000000..93aa289e4439 --- /dev/null +++ b/Documentation/x86/intel_cet.rst @@ -0,0 +1,136 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================================= +Control-flow Enforcement Technology (CET) +========================================= + +[1] Overview +============ + +Control-flow Enforcement Technology (CET) is an Intel processor feature +that provides protection against return/jump-oriented programming (ROP) +attacks. It can be set up to protect both applications and the kernel. +Only user-mode protection is implemented in the 64-bit kernel, including +support for running legacy 32-bit applications. + +CET introduces Shadow Stack and Indirect Branch Tracking. Shadow stack is +a secondary stack allocated from memory and cannot be directly modified by +applications. When executing a CALL instruction, the processor pushes the +return address to both the normal stack and the shadow stack. Upon +function return, the processor pops the shadow stack copy and compares it +to the normal stack copy. If the two differ, the processor raises a +control-protection fault. Indirect branch tracking verifies indirect +CALL/JMP targets are intended as marked by the compiler with 'ENDBR' +opcodes. + +There is a Kconfig option: + + X86_CET. + +To build a CET-enabled kernel, Binutils v2.31 and GCC v8.1 or LLVM v10.0.1 +or later are required. To build a CET-enabled application, GLIBC v2.28 or +later is also required. + +There are two command-line options for disabling CET features:: + + no_user_shstk - disables user shadow stack, and + no_user_ibt - disables user indirect branch tracking. + +At run time, /proc/cpuinfo shows CET features if the processor supports +CET. + +[2] Application Enabling +======================== + +An application's CET capability is marked in its ELF header and can be +verified from readelf/llvm-readelf output: + + readelf -n | grep -a SHSTK + properties: x86 feature: IBT, SHSTK + +If an application supports CET and is statically linked, it will run with +CET protection. If the application needs any shared libraries, the loader +checks all dependencies and enables CET when all requirements are met. + +[3] Backward Compatibility +========================== + +GLIBC provides a few CET tunables via the GLIBC_TUNABLES environment +variable: + +GLIBC_TUNABLES=glibc.tune.hwcaps=-SHSTK,-IBT + Turn off SHSTK/IBT. + +GLIBC_TUNABLES=glibc.tune.x86_shstk= + This controls how dlopen() handles SHSTK legacy libraries:: + + on - continue with SHSTK enabled; + permissive - continue with SHSTK off. + +Details can be found in the GLIBC manual pages. + +[4] CET arch_prctl()'s +====================== + +Several arch_prctl()'s have been added for CET: + +arch_prctl(ARCH_X86_CET_STATUS, u64 *addr) + Return CET feature status. + + The parameter 'addr' is a pointer to a user buffer. + On returning to the caller, the kernel fills the following + information:: + + *addr = shadow stack/indirect branch tracking status + *(addr + 1) = shadow stack base address + *(addr + 2) = shadow stack size + +arch_prctl(ARCH_X86_CET_DISABLE, unsigned int features) + Disable shadow stack and/or indirect branch tracking as specified in + 'features'. Return -EPERM if CET is locked. + +arch_prctl(ARCH_X86_CET_LOCK) + Lock in all CET features. They cannot be turned off afterwards. + +Note: + There is no CET-enabling arch_prctl function. By design, CET is enabled + automatically if the binary and the system can support it. + +[5] The implementation of the Shadow Stack +========================================== + +Shadow Stack size +----------------- + +A task's shadow stack is allocated from memory to a fixed size of +MIN(RLIMIT_STACK, 4 GB). In other words, the shadow stack is allocated to +the maximum size of the normal stack, but capped to 4 GB. However, +a compat-mode application's address space is smaller, each of its thread's +shadow stack size is MIN(1/4 RLIMIT_STACK, 4 GB). + +Signal +------ + +The main program and its signal handlers use the same shadow stack. +Because the shadow stack stores only return addresses, a large shadow +stack covers the condition that both the program stack and the signal +alternate stack run out. + +The kernel creates a restore token for the shadow stack restoring address +and verifies that token when restoring from the signal handler. + +Fork +---- + +The shadow stack's vma has VM_SHSTK flag set; its PTEs are required to be +read-only and dirty. When a shadow stack PTE is not RO and dirty, a +shadow access triggers a page fault with the shadow stack access bit set +in the page fault error code. + +When a task forks a child, its shadow stack PTEs are copied and both the +parent's and the child's shadow stack PTEs are cleared of the dirty bit. +Upon the next shadow stack access, the resulting shadow stack page fault +is handled by page copy/re-use. + +When a pthread child is created, the kernel allocates a new shadow stack +for the new thread.